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1996 Pontiac Grand Am Bucking, hesitation and backfiring.

Tiny
CEEMATT
  • MEMBER
  • 1996 PONTIAC GRAND AM
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 61,000 MILES
Hello people! My Grand Am has rough idle on and off. It was missing a lot yesterday but running smooth at idle for most of today. It bucks when cruising at low rpms on the highway half the time(somewhere between 1500 and 2000 RPMs. It takes a lot of accelerating to get it out of that slump. It also tends to buck and backfire occasionally when accelerating from a stop.

When I start it up, it starts right away, but it either hovers at 900rpms for about 3 seconds before idling normally or it will go up to 900, drop immediately down to like 400, then go to normal idle. In the 2 years I've only it, twice I've tried to start it up and it would not start unless I pumped the gas a little (once last year and once a month ago).

I haven't put new plugs and wires on it. I believe they are the originals. They might have been left because plugs used to last 100k miles. I have no check engine lights. What could this be?
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Monday, May 26th, 2008 AT 12:20 AM

2 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Do a major tune-up on it

Check these components inspect and test it the coolant temperature sensor/idle air control valve cleaned out, for the rough idle/ for the hesitation the throttle position sensor and follow it with a fuel pressure check-
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Monday, May 26th, 2008 AT 12:34 AM
Tiny
CEEMATT
  • MEMBER
  • 2 POSTS
I cleaned the IAC valve and I put a newer TPS sensor. The idle is still rough but not nearly as rough. The misses at idle doesn't feel like I hit a bump in the road anymore. There is still hesitation though, but only when the engine is under "heavy load" when cruising slightly over or downshifting from 1500rpms. I think I only felt it when the engine was warm also. Cold, I didn't feel much of anything. The fuel pressure check will be coming soon.
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Monday, May 26th, 2008 AT 11:13 PM

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